Distillation process



Nov. 10, 41942. L s, WAL-TON y 2,301,349

DISTILLATION PROCESS Filed July 29, 1939 fa 22 25 tlig/25- l 7'o WER Bo Tre M:

f8 l -Z 4 ,el/@l Patented Nov. 10, 1942 Jesse S. Walton,

Westfield, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application July 29, 1939,

1 Claim.

The present invention relates to an improved method for the distillation of oils. The invention is concerned with a distillation operation in which loss of fresh feed into side streams is prevented. VThe invention is especially directed to a process in which vapors from a petroleum oil cracking operation are segregated, one portion entering a distillation tower from which side streams free of fresh feed are withdrawn, While the other portion enters a tower where it is contacted with fresh feed.

It isvwell known in the art to distill oils, particularlyv petroleum oils, by various processes under wide temperature and pressure conditions. It is also known in the art to subject petroleum oils to elevated temperatures and pressures, as for example, in the conversion of petroleum oils into relatively higher boiling and into relatively lower boiling fractions. ln these oil cracking processes the feed material is subjected to elevated temperature and pressure conditions for various time periods which are usually measured yield per unit throughput, hereinafter termed conversion per pass. These various variable factors are optimurnly adjusted and, to a large extent, are functions of the particular feed material being processed and upon the yields and quality of the products desired. In a typical petroleum oil cracking operation, the'feed oil is introduced into the bottom of a tower. Lighter portions of the feed oil are vaporized in said primary bubble tower yand passed overhead with the cracked products. The remaining feed oil, together with cycle stock, is withdrawn from ble tower and introduced into a furnace or heating coil in which the oil is heated to cracking temperatures. The heated oil is withdrawn from the heating coil, passed into a reaction or soaking drum in which the oil is held for an additional time under cracking conditions. The cracked oil is withdrawn from the reaction drum and then passed through a pressure release valve into an evaporator. from the bottom of the evaporator, while the vaporous products are passed into the primary bubble tower in which they contact the fresh feed oil. The cracked vaporous products, together with vaporized portions of the feed oil, are removed overhead from the primary bubble tower and introduced into a secondary bubble tower. Temperature and pressure conditions of the system are usually controlled so as to remove overhead from the secondary tower a petroleum fraction boiling in the gasoline range.

in terms of p primary bubble Y the bottom of the primary bub- Tar is usually withdrawnl Heating oil Serial No. 287,271

(C1. ISB-48) fractions are withdrawn from the bottom of said secondary bubble tower and may be recycled, but are preferably further refined and used as such. The introduction of fresh feed into the yprimary tower as described results in material operating advantages. However, the operation is not entirely satisfactory since a considerable loss of fresh feed material occurs into the side streams. This is due primarily to the fact that lighter portions Yof the virgin feed oils are vaporized when they contact the hot oils from the heating coil.

I have now discovered a possible in a cracking operation to recycle material withdrawn from the cracking system consisting of the most virgin materials, while at the same time to withdraw vas aside stream for extraneus use a valuable by-product containing nothing but cyclic materialsl which have already been reacted. f

The process of my invention may be readily understood by reference to the attached drawing whichis given for the purpose of illustration and should not be construed as limiting the invention in any manner whatsoever. The figure illustrates my invention as applied to a typical petroleum oil crackingoperation. It is assumed, for the purposes of description, that the feed oil is a petroleum gas oil fraction boiling in the range from about 4007 F. to 700y F. The fresh feed oil is introduced by means of feed line i into the lower partoffractionating bubble tower 2 in which the fresh feed contacts cracked vaporous products whichare introduced into bubble tower l 2 by means of line Lighter portions of the fresh feed, together a of the cracked vaporous product, Ypass upwardly through tower 2 into a fractionatingvsectio'n. A side stream product is withdrawn from tower 2 by means' of line 4, while the uncondensed vapors are removed from towerv 2- by means of vapor line 5," The unvaporized fresh feed, together with cycle'oiLis' withdrawn from the bottom of bubble tower 2 and introduced into furnace 6 by means of line '1, Furnace 6 is designed to secure optimum Vheat transfer as the feed stock flows throughtubes in the respective sections and to bring the oil 'up to the desired temperature. The total'feed is withdrawn from furnace E by means of linesl and passedinto soaking drum or reactionchamber' 9 in which the oil is held for an additional time period under cracking conditions. The cracked oil is withdrawn from reaction drum 9 by means of line l0 and passed through pressure 'release valve Il into evaporator I2. The

process by which it is y with l uncondensed portions flashed vapors pass overhead from evaporator I2 I3, while tar of the desired gravity 1s usually removed as a bottoms from evaporator I2 by means of line I4. This product may be cooled to the desired extent by means of cooler The distributed to the controlled by adjusted on tower I to produce a bottoms heating oil cut of the desired specification which is re'- moved by means of line I9. Conditions are also adjusted on tower I5 so that a side stream cut moved overhead from tower I5 and introduced into secondary bubble tower 2I by means of line 22. Temperature and pressure conditions are adjusted in secondary tower 2I so that a petroleum fraction boiling in the gasoline range is` removed overhead by means of line 23. This fraction is condensed in cooler 25 and passed to distillate drum 24 in which the fixed gas is separated by means of line 26, while the distillate is removed by means of line 21. The bottoms from tower 2I are removed by means of line 28 and may be recycled as reflux by means of line I 8. The vaporous product from evaporator I2 introduced into tower 2 is subjected to temperature and pressure conditions so that a petroleum fraction to fractionate the vaporous product, the vapors imparting a portion of sensible and latent heat to the fresh feed, which fresh feed subsequently leaves tower 2 partially through partially through line 1 along with the cyclic material. Any material leaving tower 2 through line 4 will contain certain fractions of the fresh feed which have been vaporized and, therefore, this side stream material will cause the loss of feed which is not vaporized in tower 2 will drop into the bottom of the tower and is withdrawn through line 1, along with any reflux condensate formed in tower 2 by reflux entering through line 29. Since the material leaving tower 2 which does not enter tower y I5 is led to tower 2 in which the fresh feed serves CTI through line 1 consists of va relatively high boil- 75 ing material, it is cracked at lower temperatures than the material leaving tower 2 through line 4.

In accordance with the process of the present invention, the material leaving tower I5 through line 20 contains no of virgin fractions and consequently Would be entirely suitable for a cracking stock. Likewise, any material leaving tower I5 through line I9 would contain no fresh feed fractions, whereas the material leaving tower 2 through line 1 would contain fresh feed fractions and is tower 2 through lines 4 and 1 but also materials leaving tower I5 through lines 20 and I9.

The broad eld of this invention can be said to embrace all distilling operations wherein a recycling procedure is used, and portions of the tain no virgin fresh feed materials.

An advantage of the system described here is that in this cracking or recycling operation, the material w1thdrawn from the fractionating system to be reacted always consists of the most virgin materials, and the stocks withdrawn as side streams for extraneous use contain nothing but cyclic materials which have already been reacted at least one time.

A further advantage gained by carrying out an operation such as is described here is that maximum selectivity of cracking stocks is securedwith no contamination of heating oil streams with high quality virgin materials.

The process of the be limited by any theory or mode of operation,

I claim:

A method of converting higher boiling hydrocarbons to lower boiling hydrocarbons which comprises passing a relatively heavy hydrocarbon through a conversion zone at an elevated temperature to effect the desired extent of conversion, separating the products of conversion into vapors and liquid residue, splitting the vapors into two portions, fractionating one portion of vapors in a fractionating zone to separate condensate oil from overhead vapors, the condensate oil containing only constituents which have passed through said conversion zone and adapted for use as a heating oil, passing the other portion of reaction product vapcrs to a second fractionating rate overhead vapors from condensate oil containing unvaporized constituents from the fresh feed, passing the last mentioned condensate oil to said conversion zone and treating the overhead vapors from said fractionating 'zones to separate a light hydrocarbon mixture containingl gasoline constituents, the overhead vapors from a said fractionating zones being passed to a third fractionatng zone and fractionated to separate another condensate oil from a light hydrocarbon mixture containing gasolineV constituents and passing the last mentioned condensate oil as reflux to at least one of said rst two fractionating zones.

JESSE S. WALTON. 

